1. Field of the Invention
This invention relates to a force-receiving plate for a friction device such as a clutch mechanism.
2. Description of the Prior Art
A known example of force-receiving plate of this type includes an annular portion having a friction surface that contacts a friction disk secured to a driven member and pawl portions formed on the outer periphery of the annular portion for engaging a driving member. The torque of the driving member is transmitted to the driven member via the friction disk by achieving frictional engagement with the friction disk.
In the conventional force-receiving plate, the side opposite that on which the friction surface is formed is provided with reduced-thickness surface portions to avoid interference with other parts, which would otherwise result from the placement of parts within a friction device for an automatic transmission, and to assure the necessary mechanical strength. Examples of this are a force-receiving plate disclosed in the specification of Japanese Patent Laid-Open Publication (KOKAI) No. 62-274122 and a force-receiving plate disclosed in the specification of Japanese Utility Model Publication (KOKOKU) No. 5-17490. In the former, plate thickness is reduced from a point approximately halfway along the annular portion to the pawls to provide a relief for the plate thickness of a snap ring, which is for engaging the force-receiving plate with a drum of the friction device. In the latter, the arrangement is such that the thrusting force of a piston is received via a saucer-shaped spring. In this arrangement, a portion for receiving the thrusting force is formed and a relief is provided to avoid interference with the saucer-shaped spring. In a further example of a force-receiving plate of a clutch or the like, it has been proposed to provide the side opposite that on which the friction surface is formed be provided with reduced-thickness surface portions or depressions owing to a requirement that the necessary strength be assured while reducing inertial weight. In general, the reduced-thickness surface portions are formed by grinding, which is a very laborious and time-consuming task.
Further, it is requested that the pawl portions of the force-receiving plate has a strength or hardness sufficient to receive a rotational torque from the driving member and the annular portion having the friction surface has a hardness over a predetermined value in view of a friction with the friction disk. In fact, the force-receiving plate is axially thrusted out by a hydraulic piston while receiving the frictional torque through the pawl portions which are arranged in grooves formed on the driving member. As a result, wear of the pawl portions is considerably large. Furthermore, a clearance between each pawl portion and each groove for allowing the force-receiving plate to move along the groove is necessary and hence the pawl portions impact against the side walls of the grooves when the fluctuation of the rotational torque occurs or the rotation of the driving member is reversed. Thus, the pawl portions must have a hardness enough to withstand these phenomenons. To provide the force-receiving plate having sufficient hardness, a normal steel plate material is punched in the form of the force-receiving plate and subsequently such the plate must be subjected to an induction hardening or a caburizing hardening. This results in deformation of the force-receiving plate.